Injection molding of plastic ammunition case



Dec. 1, 1964 e. HERTER INJECTION MOLDING OF PLASTIC AMMUNITION CASEFiled Dec. 12. 1960 2 Sheets-Sheet l T L1: u

Dec. 1, 1964 G. L. HERTER INJECTION MOLDING 0F PLASTIC AMMUNITION CASEFiled Dec. 12, 1960 2 Sheets-Sheet 2 "My? M ,4 TTO/PIVEXS United StatesPatent answer WEMITIQNMELDWG 0F PLASTEO AlViLMUNl'litBN CAtlll George L.Herter, @29 3rd Ave. NE, Waseea, Minn. Filed Dec. 12, 1965), Ser. No.75,395 5 Claims. (Cl. 264- 328) is substantially without support, suchan automatic shotguns.

While the process and structure of my invention is particularlyapplicable to shotgun shells, it is well adapted with integrated tubularreinforcing zone-sections for small arms ammunition and for shell casesof relatively large size used for field artillery and naval purposes. I1

in the manufacture of present conventional shotgun shells the greaterportion of thecylindrical case is constructed from a tube impregnatedwith paraffin or the like, in some instances a plastic tube, and suchtube is telescoped within the sleeve portion of a metallic base member.The sleeve-portions of such metallic base members in not only shot unshell cases, but other small arms and smaller artillery shells are veryexpensive to manufacture, requiring a large number of draw operationswhich prohibit the use of relativelyinexpensive tubularly formed metalstock. s

In the case of shotgun shells, connection is made between the telescopedcardboard or plastic tube and V the open portion of the metallic sleeveby crimping the metal inwardly against sleeve and telescoped caseportion or by crimping the paper tube into the metal base. Such crimpinginwardly of the wall ofthe metal sleeve of course deforms said walls andalso the interconnected portion of the cardboard case and the juncturesurfaces are not smooth and continuous, resulting in a far-fromperfectseal between metal sleeve and cardboard tube or case. If a plastic tubeis used with a metal base, in all instances known at this time, the sealis imperfect and mois ture penetrates between the metal sleeve and theinterconnected end of the plastic tube.

As is well known, even though the tubular case portions of conventionalshotgun shells and the like are heavily impregnated with paraffinorother moisture-resistance I :iaterial, theywill swell and deform whensubjected to moisture for even relatively short periods, and permitpenetration of moisture within the case. Thereafter, trouble suchasjamming in the loading of the magazine, or in the subsequent positioningof shell in breech, or in ejection after firing, often occurs.

it is an object of my invention to provide an integrally molded plasticammunition case or shell, having Wide application for'small armsammunition, and naval or artillery projectile cases with an integralcircular base plate or heavy'plastic web, having an ejection rim and anintegrally formed elongatedtubular shell, and capable when desired, ofbeing integrated with one or more, zonereinfor cing sleeves constructedof metal or other strong reinforcing material which may be inexpensivelyobtained on the market as tubular stock.

A further object the manufacture and provision of an integral plasticammunition case of the class described wherein a reinforced circularbase plate and elongated cylindrical case extending therefrom, arecontinuous and integrated, requiring no crimping or other connection ofparts and preferably presenting both externally and internally, smooth,generally cylindrical surfaces without seams.

Another object is the provision of an injection-molded,

integral plastic shell case which in addition to integral con tinuoustubular walls has an inherently provided reinforced axial portion in thecircular base plate for insertion and support of the primer; andwhichmay be manufactured commercially at low cost by flowing or gatingplastic in fluid state to eliminate all seams, and where desired, ridgesand discontinuous internal and external surfaces.

A still further object is the manufacture of plastic ammunition cases orshells of the class described which are particularly well adapted forreloading; which will not be distorted or swelled by moisture, nor allowmoisture seepage between a plastic tube and metallic base, and which mayoften employ a reinforcing base sleeve memoer constructed of metal orother relatively inexpensive tubular stock, said reinforcing sleeve atleast partially covering the edge of the rim of the plastic base plateor thickened web and if desired, covering all said rim and encirclingthe same and even covering the base plate, to strengthen the baseportion of the shell and protect the edge of the rim so that the ejectorof a gun will not damage the same.

A further object is the provision of a novel and efiicient process, ofmold and die procedure and steps, with gated injection of a plasticfluid before hardening, to cause the case of the shell to be perfectlyformed with flow of the tube uniformly, first radially and outwardlyfrom the injection point through the base plate or web, and thenuniformly and tubularly forward through the cylindrical case portion ofthe shell.

Another important object is the provision of a process of the typedescribed wherein one or more zone-reinforcing sleeves, or a completebase reinforcing section may be embodied in the integrated shell byinsertion of a metallic tube, or reinforced plastic fiber tube incertain of the mold cavities before injection of the plastic in fluidstate,

and in fact, cooperating with certain mold surfaces to 1 provideadditions to the overall molding surfaces and whereby the interior wallof the shell from base plate to I the outer filling end is continuousand smooth, and the successful injection molding and die apparatus forcarrying out my novel, process shown in therfirst or mo1d-separatedpositions of the parts; I 9

FIG. 2 is a section taken generally along the line 2-2 of FIG. 1,saidsection being offset as more accurately shown on the section, line22 of FIG. 4; 1 FIG. 3 is a fragmentary longitudinalsection with themovable molding and die elements retracted for removal of -acompletedshell and/ or for insertion of a metallic base-reinforcing sleeve, priorto telescoping or compacting of said mold and die elements;

'FIG. 4 is a rear end elevation of the mold machine or --apparatus;

FIG. 5 isa front end elevation of the same;

' {FIG 6 is a cross section takendiametric'ally and longitudinallythroughia completed rnolded' shell comprising 3,15%,7dl Patented Dec. 1,1964 FIG. 8 is a longitudinal section taken diametrically showinganother form of my improved plastic shell; and

FIG. 9 is a cross section taken on the line 99 of FIG. 8; and

FIG. 10 is a longitudinal section taken diametrically through a longrifie shell case.

Referring now to the form of ejection molding machine or apparatusillustrated and by which my novel process may be successfully practiced,provision is made as shown, for simultaneously molding four shotgunshells S although it will of course be understood that the mold and dieelements, sprues or injection passages and cooling media might bemultiplied or reproduced, to of course manufacture simultaneously, asubstantially greater number of shells.

Essentially the machine or apparatus illustrated in the drawingscomprises three mold die-heads indicated as entireties by the letters A,B and C, one of which, A, contains the external base-molding die 11 andas shown is stationary. The intermediate die-carrying head B hasreplaceably mounted therein the external shell-case-mold die 12 and saidhead is mounted for longitudinal movement relative to head A. The thirdhead C has accurately and removably mounted therein the stud die 13 forforming the interior, smooth cylindrical surface of the shell case andwhich has a cup-forming die section 13a at its inner or protruding endfor molding the interior of an important base-reinforcing primer pocket.Head C, as clearly shown in FIG. 3 may be retracted substantially beyondthe extreme retracted position of head B.

Plastic injection passages 14 formed in the stationary portion of themold machine (which has attached thereto, the head A) communicate withan axially disposed sprue member 15 for each shell production, removablyconnected with an intermediate heavy bar A-1 of the head A. The forwardand reduced tip of the sprue 15 interfits with a circularly recessed,axial portion of base die 11 to properly gate and control the injectionof plastic fluid to cause flow thereof uniformly and radially of thesprue discharge when shell-case-die 12 is thrust inwardly into operativemolding poistion as shown in FIG. 2. The gating of the injected plasticfluid then causes fiow of the plastic material in tubular formlongitudinally and outwardly between the internal, substantiallycylindrical molding surface of the shell-case-die 12 and the externalgenerally cylindrical surface of the stud die 13.

In the injection of the plastic material in fluid form inwardlongitudinal retractive movements of the heads B and C are correlatedand timed by suitable mechanism (not shown), so that the inner extremityof the shell-casedie 12 abuts against an internal, annular shoulder 11aof the base die 11, just prior to the initial injection of the plasticinto die 11 and sequentially a slight time interval before the stud die13 carried by head C moves to its extreme inward position.

It will be understood that head C with the stud die 13 moves inwardlywith the head B to define, with the internal molding surface 12a of die12, an annular thin plastic-receiving mold cavity. The plastic material,in fluid state, flows longitudinally and outwardly in tubular form tosubstantially fill said annular space between the molding surfaces ofdies 12 and 13 prior to the final inward projection of the stud die 13;whereafter the stud die is moved inwardly to its extreme positionleaving its forward extremity in slightly spaced relation to a specialslightly recessed base-rim-molding portion 11b of the base die 11. Anannular mold-groove 13b is formed concentrically in the inner end of thecup-forming section 13 of stud die 13, cooperating with the slightlyrecessed base rim molding portion 11b of die 11 to produce in thefinished shell, a somewhat thickened base plate a and an integralannular primer pocket 2%, as shown in FIGS; 6 to 8. At the innerextremity of the shell-case-die 12, the internal bore is beveled for aslight distance forming a narrow molding annulus 12b which cooperateswith the base rim molding portion 11b of die 11 to provide for and moldthe plastic rim 20r of the base web of the shell.

The circumference of the molding surface 130 from the extremity of studdie 13 rearwardly for the requisite length of a reinforcing metal sleeveis reduced as shown, whereby such a sleeve, designated 21 in the shellof FIG. 6 will be externally and very snugly accommodated in theterminal interior of the bore of molding surface 12a of theshell-case-die 12, with the diminished surface 13c in operative moldingrelation spaced slightly therefrom to provide an integral tubularplastic connection between the thickened base plate 20a of the shell andthe uncovered portion of the tubular plastic shell case 200. Thefunctional flow of the gated, ejected plastic material with theattendant inward movement of the projecting portion of the stud die 13and the diminished external molding surface 13c causes outward radialforce internally of the reinforcing metal sleeve 21 (which becomes partof the molding surface internally) and positively prevents any flow ofthe plastic material externally of metal sleeve 21; and simultaneouslyproduces intimate crowding and sealed contact between the cooperating,slightly thickened sleeve portion 20s of the plastic case and the metalreinforcing sleeve 21.

The apparatus includes a synchronized injection control valve (notshown) which is timed and controlled to shut off, thus stopping thecycle of ejection of the plastic in fluid state just prior to theinstant stud die member 13 is completely ejected rearwardly with theforward terminal 130. then in abutment with the orifice constituting theejection channel of the sprue 15.

The cycle of operation then includes a holding or retaining step withthe mold parts compacted as shown in FIG. 2, during which time theplastic material then perfectly formed cures or hardens. Thereafter inthe cycle of operation the die carrying heads B and C move axially intothe ultimate separated positions as shown in FIG. 3.

It is important that a water jacket or cooling means may be provided forcirculating a coolant through the jaws and surrounding portions. Severalwater passages are shown all indicated by the letter W whichinterconnect with the circulated source of refrigerant or coolant. It isimportant that the interior of the stud die 13 be cooled and to this enda longitudinal axial passage 13d is formed throughout the greater lengthof the stud die 13 communicating at its outer end with one of the waterpassages W.

In the apparatus shown air pressure is applied from peripheral portionsof the free end of stud die 13 through a series of diagonal radial portsor air passages 13e.

Air supply tube 22 connected with air supply passage A communicates withports 13a. As shown air pressure from 13:: provided for additionaloutward pressure against the base sleeve portion of the plastic casecausing the same to be pressed firmly against the material reinforcingsleeve 21.

From the foregoing and inspection of FIGS. 2 and 3 of the drawings itwill be seen that under pressure during the ejection or mold fillingstep of my process, the plastic in fluid state ejects from the forwardorifice of sprue 15 entering the annular mold cavity and die 11 asrelated with the opposing end of molding die 12. The ejected fluiddisperses or proceeds to flow uniformly and radially outward from thedischarge of the sprue nicely filling the shallow circular base platemold cavity 11b and then through the cooperation of the interior studdie 13 and its surrounding external forming die 12 flowing uniformly ina tubular extrusion into the very thin tubular mold cavity to form thegreater part of the length of the cylindrical shell case. The outer endof this thin tubular molding cavity is closed to leave an opening in theshell when the mold carrying dies B and C are fully compacted in theposition shown in FIG. 2.

Referring now to the shells shown in FIGS. 6 to 9 are particularlysuitable for shotgun shellc ases and when on larger scale with somesmall variations can be utilized for artillery or naval projectileshells.

The shells shown in FIGS. 6 and -7 it will be noted has the thickenedcircular base plate Zita (not reinforced by metal or otherreinforcingmeans). The interior shell surface includes the base plate tothe outer open end of the shell and is a continuous smooth plasticsurface Without interruption and has no scams or ridges although ifdesired the diameter of the plastic sleeve portion Ztls could besomewhat diminished relative to the exposed greater length of the caseportion. Reinforced primer pockets 20b of tubular form are integrallyprovided in both types of shells shown in FIGS. 7 to 9 inclusive,serving not only to perfectly center and hold the primer but also tosubstantially reinforce the entire base plate.

In the shell of FIGS. 6 and 7 the metallic reinforcing sleeve 21 hasrim-edge engaging portions 214: which at least partially cover the edgesof rim 24. It will of course be understood that the reinforcing sleeves21 may have flanges 21a which completely or partially encircle the edgeof the plastic rim Ztlr and/or which makes them even under the exposedbase plate or may cove parts of the entire base plate Ztla.

In the shell of FIGS. 8 and 9 a complete reinforcing metal base isillustrated. It will of course be understood that the reinforcingsleeves 21 may be constructed of other suitable materials such as fiberplastic instead of metal.

In FIG. 10 a rifle shell case is illustrated in axial longitudinalsection. Here the base portion of the plastic shell is generally similarto that shown in FIGS. 7 and 8.

The plastic case for use in long rifle ammunition has a diminished outertubular portion 24a which is reinforced by, as shown, a metalZone-reinforcing sleeve or ring 26.

It will be understood that with the metallic reinforcing dinaryrelatively cheap tubular metallic or reinforced plastic stock can beutilized at great saving.

I have found that many: types of plastic material are suitable forcarrying out my new process and for producing my new articles ofmanufacture. Both. thermoplastic and thermo-setting plastics underproper conditions may be utilized. I have found linear polyethylenesvery satisfactory for my purposes. Also, butyrate and polyethylene maybe successfully employed.

From the foregoing description it will be seen that I have providedefficient and relatively inexpensive plastic cases for ammunition ofnumerous types, adapted to be integrated with metallic or otherreinforcing sleeves of comparatively inexpensive construction at desiredzones (base, projectile accommodating or other in the casing). It willbe understood that my invention is equally applicable without the use ofmetallic or other zone-reinforcing sleeves.

It will be further appreciated that l have provided a commerciallyoperative simple injection molding process for manufacture of saidimproved ammunition cases, said process throughout the closelycooperating steps of ejection, gating and subsequent uniform tubularflow of the plastic in fluid state. assures continuity of all internaland external s eliminating longitudinal seams and when desired, allridges in the case-itself. v

It will,.of course, be understood that various changes may be made inthe form, details, arrangement and 'proportions of the various partswithout, departing from the scopeof my invention.

What is claimed isi V V '1. The process of manufacturing integralammunition cases by plastic injection molding, which consists in axiallyurfaces of the produced plastic molding,

gating plastic material uniformly in fluid state through a thin tubularmold cavity outwardly from the injection source to form the elongatedcase of a shell, and prior to said tubular fiow, gating said plasticmaterial radially outward through a transverse mold cavity communicatingwith said tubular mold cavity said material flowing axially into saidcavity from an open circular sprue to form an integrally connectedshell-base-plate, provided with a rim edge, and while gating saidplastic material through said transverse mold cavity, simultaneouslyapplying axial pressure toward said injection source in said transversemold .cavity to substantially assist in the flow of said plasticmaterial radially outward from said injection source, stopping the flowof said plastic material when said mold cavities are filled andproducing the hardening of the material in the filled mold cavities.

2. The process of manufacturing integral ammunition cases, by plasticinjection molding, which consists in injecting and axially gating anduniformly extruding plastic material in fluid state into an ultimate,elongated, thin tubular mold cavity defined by relatively longitudinallymovable inner cylindrical stud and outer substantially concentric diemembers, said outer die member having cooperating therewith an abutmentend surface spaced from the inner extremity of said inner die member toprovide an integral base plate in the plastic case, simultaneouslyapplying pressure oppositely from the injection of said plastic materialand from the telescopic longitudinal movement of said inner stud diemember relative to said outer die member, causing iiow of said injectedmaterial first uniformly radially through the area of said base web andthen longitudinally and uniformly forward and outwardly through saidthin tubular mold cavity to positively assure smooth, continuous innerand outer, generally cylindrical surfaces on. the tubular case formed.

3. The process set forth in claim 1 further characterized by integrallydefining and filling of a small integral cylinder-shaped mold pocketaxially and internally of the base section of the case through provisionof an annular mold channel concentrically disposed at the innerextremity of said inner die member in cooperation with said end moldcavity comprising a circular base plate section communicating near itsperipheral edge with a for-. wardlyand perpendicularly extending thintubular passage, 7 said axial pressure injection being accompanied bysimultaneous pressure movement of a cylindrical stud die member towardsaid circular plate section and the end of said nozzle, I therebycausing initial fiow of plastic fluid uniformly and radially outwardfrom said axis of injection, then uniformly in outward annular extrusionthrough said tubular mold cavity, and continuing pressure movement ofsaid stud die member until the extremity thereof substantially abuts vthe forward extremity of said nozzle. 7 5. The process set forth inprevious, claim 4 wherein said cylindrical stud die member at itsforwardoperating end carries a cylindrical projection for substantiallyabutting the forward extremity of said nozzle in full operativeposition,

and provides a small concentric annular mold passage surrounding saidprojection for forming an integral apertured cylindrical reinforcing andprimer-containing 'element extending axially and concentrically of saidcircular platesection.

(References on'following page) References Cited in the file of thispatent UNITED STATES PATENTS Oldham June 13, 1939 Tackler Mar. 12, 1940Wiley June 5, 1945 Morin Nov. 13, 1945 Stacy Apr. 15, 1947 Paulve July27, 1954 8 Wilson Jan. 4, 1955 Morin Jan. 14, 1958 Lefebvre June 16,1959 Fitzsimmons et a1 Feb. 28, 1961 Seymore Mar. 6, 1962 Sherman Mar.29, 1962 FOREIGN PATENTS Great Britain Mar. 30, 1944

1. THE PROCESS OF MANUFACTURING INTEGRAL AMMUNITION CASES BY PLASTICINJECTION MOLDING, WHICH CONSISTS IN AXIALLY GATING PLASTIC MATERIALUNIFORMLY IN FLUID STATE THROUGH A THIN TUBULAR MOLD CAVITY OUTWARDLYFROM THE INJECTION SOURCE TO FORM THE ELONGATED CASE OF A SHELL, ANDPRIOR TO SAID TUBULAR FLOW, GATING SAID PLASTIC MATERIAL RADIALLYOUTWARD THROUGH A TRANSVERSE MOLD CAVITY COMMUNICATING WITH SAID TUBULARMOLD CAVITY SAID MATERIAL FLOWING AXIALLY INTO SAID CAVITY FROM AN OPENCIRCULAR SPRUE TO FORM AN INTEGRALLY CONNECTED SHELL-BASE-PLATE,PROVIDED WITH A RIM EDGE, AND WHILE GATING SAID PLASTIC MATERIAL THROUGHSAID TRANSVERSE MOLD CAVITY, SIMULTANEOUSLY APPLYING AXIAL PRESSURETOWARD SAID INJECTION SOURCE IN SAID TRANSVERSE MOLD CAVITY TOSUBSTANTIALLY ASSIST IN THE FLOW OF SAID PLASTIC MATERIAL RADIALLYOUTWARD FROM SAID INJECTION SOURCE, STOPPING THE FLOW OF SAID PLASTICMATERIAL WHEN SAID MOLD CAVITIES ARE FILLED AND PRODUCING THE HARDENINGOF THE MATERIAL IN THE FILLED MOLD CAVITIES.